Currently, U.S. Air Force crewmembers wear either PCU-15 or PCU-16 parachute harness assemblies while in flight. Such parachute harness assemblies have the primary functions of distributing parachute opening shock loads onto the human body and of suspending the user beneath the inflated parachute canopy after an ejection has taken place. These parachute harnesses are not designed to provide means for retaining the crewmembers in their respective aircraft seats during normal flight. Instead, all U.S. Air Force aircraft ejection seats are provided with a lap belt assembly and two inertia reel shoulder restraint straps to restrain crewmembers in their seats.
These two inertia reel straps have manual and automatic modes. While in the manual mode, the straps can be locked and unlocked by the seat occupant. In the automatic mode, the straps will lock when the negative Gx (forward) acceleration exceeds a set threshhold or when the strap and reel velocity exceeds a set threshhold level. However, the inertia reel straps do not apply any downward forces on the shoulders of the crewmembers and must not apply any such force in accordance with the controlling military specifications. This is because any downward loading directly on the shoulders may compress the spine and increase the risk of spinal injury in certain situations, for example, in an ejection. As a result, the inertia reel straps do not provide negative Gz (upward) restraint until the crewmember has moved upward off the seat pan a considerable distance even when the reel strap locking mechanism is locked. For small crewmembers, this distance can be over five inches.
Thus, the lap belt assembly is the only effective negative Gz restraint provided to crewmembers wearing the harness and lap belt assemblies currently employed by the U.S. Air Force.
The lap belt assembly is incorporated into the Advanced Concept Ejection Seat-II (ACES-II) currently employed by the U.S. Air Force in most of its new aircraft. The lap belt assembly is anchored to the aircraft seat at the seat back such that in normal use the lap belt is oriented at an angle less than 45.degree. above the seat pan. Due to this arrangement, the lap belt provides both negative Gx and negative Gz restraint to the seat occupant's thighs and lower torso. However, even with the lap belt tight, a crewmember will still move upward off the seat pan when undergoing negative Gz acceleration, since the seat belt will rotate to a more upward angle with respect to the seat pan. This upward movement, when combined with the natural elongation of the human spine, can result in the head of the crewmember moving upward over five inches. Also, even with the lap belt tight, there is very little Gy (lateral) support of the crewmember's shoulders or upper torso.
While it is desirable to wear the lap belt as tight as possible to limit negative Gz movement, wearing the belt tight will reduce the aftward viewing ability of the crewmember (also referred to as "check six" capability). This affects the pilot's efficiency in combat maneuvers since the pilot desires full aftward viewing. Thus, many pilots and crewmembers develop the habit of flying with the lap belt loose so that it does not affect their aftward viewing ability. With the lap belt loose, the upward movement of the crewmember during negative Gz acceleration increases even more, and contact of the helmet with the cockpit canopy is common.
In the ACES-II, the survival kit is located under the seat pan. The survival kit is attached to the PCU-15 or PCU-16 parachute harness by adjustable side straps which extend from the kit under the seat pan up to the harness. Some crewmembers tighten these side straps to limit their potential Gz movement. However, in doing so, the rotation of the upper torso or shoulders is severely limited, and the "check six" capability is essentially eliminated. Also, any negative Gz acceleration will result in forces being applied to the seat pan, which is not structurally capable of supporting large upward forces.
The ACES-II includes a mechanism for automatic release of the lap belt anchor fittings as well as the two inertia reel straps after the crewmember has ejected. When this mechanism is released, the crewmember is free to separate from the seat. Since the survival kit is attached to the crewmember's harness, the survival kit will also separate from the seat.
It is clear that there is a need for an improved harness and belt assembly which will adequately restrain the movement of the crewmembers in all directions, including the negative Gz direction while not limiting the torso rotation of the crewmember to "check six", i.e. without affecting the aftward viewing ability of the crewmember.
This need has become more critical in view of the increased performance levels of military aircraft. The basic design of the PCU-15 or PCU-16 harnesses is now over thirty years old. While some improvements have been made to the lap belt and inertia reel shoulder restraint strap systems during this time, there has been little if any functional improvement in the Gy or negative Gz restraint afforded by these systems.
This invention addresses this need in the art, as well as other needs which will become apparent to those skilled in the art once given this disclosure.